Conventionally, an SCR (Selective Catalytic Reduction) device has been known as a device for purifying nitrogen oxide (hereinafter described as NOx) in exhaust gas emitted from an engine.
The SCR device injects a reducing agent (for example, ammonia or the like) to an exhaust path of the engine to make NOx in the exhaust gas and the reducing agent to react on a catalyst, thereby reducing and purifying NOx.
To control an engine equipped with such an SCR device, for example, Japanese Patent Laying-Open No. 2005-147118 (Patent Document 1) discloses an exhaust gas purification device for an engine that urges a driver to have an SCR device repaired immediately when an abnormality occurs in the SCR device and provides appropriate management of the SCR device. The exhaust gas purification device for an engine includes reducing agent addition means adding a reducing agent for NOx to exhaust gas from the engine, abnormality detection means detecting occurrence of an abnormality in the reducing agent addition means, and engine control means providing control, when occurrence of an abnormality is detected by the abnormality detection means, to limit operation of the engine, or to set output characteristics of the engine with respect to accelerator operation by the driver to be different from those in normal operation other than operation at the time of occurrence of an abnormality.
According to the exhaust gas purification device for an engine, when an addition device has an abnormality and cannot add an appropriate amount of the reducing agent to the exhaust gas, operation of the engine is limited, for example, restart of the engine that has been once stopped is disabled. Thereby, traveling in a state where NOx is not sufficiently purified can be limited, and the driver can be urged to have the addition device repaired. Further, in addition to or instead of limiting operation of the engine, by changing the output characteristics of the engine with respect to the accelerator operation, for example, by decreasing a fuel injection amount set for the same amount of accelerator operation to be smaller than that in normal operation, traveling can be limited and the driver can be urged to have the addition device repaired.
Patent Document 1: Japanese Patent Laying-Open No. 2005-147118